Sensor array with split-drive differential sensing

ABSTRACT

A device for capacitive sensing includes: a plurality of sensor electrodes, the plurality of sensor electrodes comprising: a plurality of receiver electrodes and a plurality of transmitter electrodes, wherein a transmitter electrode of the plurality of transmitter electrodes comprises a first portion and a second portion with a separation between the first portion and the second portion; and a processing system, configured to: drive the first portion of the transmitter electrode with a transmitter signal, receive a resulting signal corresponding to the first portion of the transmitter electrode via a first receiver electrode of the plurality of receiver electrodes, receive a reference signal corresponding to the second portion of the transmitter electrode via a second receiver electrode of the plurality of receiver electrodes, and determine a modified resulting signal based on the resulting signal and the reference signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation-in-part of copending U.S.patent application Ser. No. 14/674,623, filed Mar. 31, 2015, which isincorporated herein by reference in its entirety.

BACKGROUND

Input devices including proximity sensor devices (also commonly calledtouchpads or touch sensor devices), as well as fingerprint sensors, arewidely used in a variety of electronic systems. Proximity sensor devicestypically include a sensing region, often demarked by a surface, inwhich the proximity sensor device determines the presence, locationand/or motion of one or more input objects. Fingerprint sensors alsotypically include a sensing region in which the fingerprint sensordetermines presence, location, motion, and/or features of a fingerprintor partial fingerprint.

Proximity sensor devices and fingerprint sensors may be used to provideinterfaces for the electronic system. For example, proximity sensordevices and fingerprint sensors are often used as input devices forlarger computing systems (such as opaque touchpads and fingerprintreaders integrated in, or peripheral to, notebook or desktop computers).Proximity sensor devices and fingerprint sensors are also often used insmaller computing systems (such as touch screens integrated in cellularphones). Such devices and sensors are often susceptible to a variety oftypes of noise. In certain instances, signal quality is significantlydegraded if such noise is not rejected by the system.

SUMMARY

In an exemplary embodiment, a device for capacitive sensing includes: aplurality of sensor electrodes, the plurality of sensor electrodescomprising: a plurality of receiver electrodes and a plurality oftransmitter electrodes, wherein a transmitter electrode of the pluralityof transmitter electrodes comprises a first portion and a second portionwith a separation between the first portion and the second portion; anda processing system, configured to: drive the first portion of thetransmitter electrode with a transmitter signal, receive a resultingsignal corresponding to the first portion of the transmitter electrodevia a first receiver electrode of the plurality of receiver electrodes,receive a reference signal corresponding to the second portion of thetransmitter electrode via a second receiver electrode of the pluralityof receiver electrodes, and determine a modified resulting signal basedon the resulting signal and the reference signal.

In another exemplary embodiment, a processing system for a capacitivesensing device includes a processor and a memory, wherein the processoris configured to: drive a first portion of a transmitter electrode ofthe capacitive sensing device with a transmitter signal; receive aresulting signal corresponding to the first portion of the transmitterelectrode via a first receiver electrode of the capacitive sensingdevice; receive a reference signal corresponding to a second portion ofthe transmitter electrode of the capacitive sensing device via a secondreceiver electrode of the capacitive sensing device, the second portionof the transmitter electrode being separate from the first portion ofthe transmitter electrode; and determine a modified resulting signalbased on the resulting signal and the reference signal.

In another exemplary embodiment, a method for capacitive sensing for acapacitive sensing device includes: driving, by a processing system ofthe device, a first portion of a transmitter electrode of the devicewith a transmitter signal; receiving, by the processing system, aresulting signal corresponding to the first portion of the transmitterelectrode via a first receiver electrode of the device; receiving, bythe processing system, a reference signal corresponding to a secondportion of the transmitter electrode of the device via a second receiverelectrode of the device, the second portion of the transmitter electrodebeing separate from the first portion of the transmitter electrode; anddetermining, by the processing system, a modified resulting signal basedon the resulting signal and the reference signal.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary environment for an inputdevice such as a touchpad sensor;

FIG. 2 is a block diagram of an exemplary environment for an inputdevice such as a biometric sensor;

FIGS. 3A-3B are schematic diagrams of a processing system for an inputdevice using a pattern-dependent reference;

FIG. 4 is a schematic diagram of a processing system for an input deviceusing a fixed reference according to an exemplary embodiment;

FIG. 5 is a schematic diagram of a processing system for an input deviceusing a fixed reference according to another exemplary embodiment;

FIGS. 6A-6B are schematic diagrams of a processing system for an inputdevice using a fixed reference with differential adjacent readoutaccording to another exemplary embodiment;

FIG. 7 is a schematic diagram of a processing system for an input deviceusing a fixed reference with differential adjacent readout according toanother exemplary embodiment;

FIG. 8A-8B are schematic diagrams of arrays of transmission and receiverlines for a processing system for an input device in an exemplaryembodiment;

FIGS. 9A-9B are schematic diagrams of an array of transmission andreceiver lines for a processing system for an input device in anotherexemplary embodiment;

FIGS. 10A-10B are flowcharts illustrating processes for obtaining animage by a processing system for an input device in an exemplaryembodiment; and

FIGS. 11A-11B are flowcharts illustrating processes for obtaining animage by a processing system for an input device in an exemplaryembodiment.

FIG. 12 is a schematic diagram of an array of receiver and transmissionlines for a processing system for an input device in an exemplaryembodiment utilizing split-drive differential sensing.

FIG. 13 is a schematic diagram of an array of receiver and transmissionlines for a processing system for an input device in another exemplaryembodiment utilizing split-drive differential sensing.

FIG. 14 is a schematic diagram of an array of receiver and transmissionlines for a processing system for an input device in another exemplaryembodiment utilizing split-drive differential sensing.

FIG. 15 is a schematic diagram of an array of receiver and transmissionlines for a processing system for an input device in another exemplaryembodiment utilizing split-drive differential sensing.

FIG. 16 is a schematic diagram of an array of receiver and transmissionlines for a processing system for an input device in another exemplaryembodiment utilizing split-drive differential sensing.

FIGS. 17A-C are schematic diagrams of an array of receiver andtransmission lines for a processing system for an input device inanother exemplary embodiment utilizing split-drive differential sensingshowing an exemplary way of operating the array to obtain readings forthe top half of the array.

FIGS. 18A-C are schematic diagrams of the array depicted in FIGS. 17A-Cshowing another exemplary way of operating the array to obtain readingsfor the top half of the array.

FIG. 19 illustrates an exemplary electrode configuration havingelectrodes with diamond patterns.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature. Thereis no intention to be bound by any expressed or implied theory presentedin the present disclosure.

Particularly in fingerprint sensors, or other sensors where the patternbeing sensed is likely to cover a large portion of the sensor, noise isintroduced throughout (e.g., finger-coupled noise in the case offingerprint sensors). Rejection of such noise by the sensor deviceallows for better signal quality to be obtained for the pattern beingsensed (e.g., for a fingerprint or any other pattern).

Additionally, with respect to certain fingerprint sensors, one aspect ofperformance may be characterized in terms of false acceptance rate (FAR)or false rejection rate (FRR). Exemplary embodiments described hereininclude fingerprint sensor configurations which reduce FAR and FRRrelative to conventional configurations. The performance of certainfingerprint sensors, e.g., in terms of FAR and FRR, may be degraded byimage distortion due to the use of a pattern-dependent reference for theanalog front-end (AFE)—for example, for a sensor with a grid oftransmission (TX) and receiver (RX) lines, the output on a particular RXline corresponding to a TX line is compared with outputs on other RXlines corresponding to that TX line (e.g., the average of the outputs onthe other RX lines) to obtain the output corresponding to a particularcoordinate of the grid. This pattern-dependent reference significantlyvaries for each TX line and slightly varies between RX lines for each TXline. As a result, even if noise from the circuit is zero, a non-randomFAR and/or FRR degradation is present (and thus cannot be improved byaveraging frames or using code division multiplexing (CDM)). Exemplaryembodiments include fingerprint sensor configurations which avoid theimage distortion associated with pattern-dependent references, so as toreduce FAR and FRR. The sensor configurations are also usable in othertypes of proximity sensor devices, such as capacitive touch pad sensors,to facilitate reduction of system-based noise.

Turning now to the figures, FIG. 1 is a block diagram of an exemplaryenvironment for an input device 100, usable in accordance with variousconfigurations of the sensors described herein. The input device 100 maybe configured to provide input to an electronic system (not shown). Asused in this document, the term “electronic system” (or “electronicdevice”) broadly refers to any system capable of electronicallyprocessing information. Some non-limiting examples of electronic systemsinclude personal computers of all sizes and shapes, such as desktopcomputers, laptop computers, netbook computers, tablets, web browsers,e-book readers, and personal digital assistants (PDAs). Additionalexample electronic systems include composite input devices, such asphysical keyboards that include input device 100 and separate joysticksor key switches. Further example electronic systems include peripheralssuch as data input devices (including remote controls and mice), anddata output devices (including display screens and printers). Otherexamples include remote terminals, kiosks, and video game machines(e.g., video game consoles, portable gaming devices, and the like).Other examples include communication devices (including cellular phones,such as smart phones), and media devices (including recorders, editors,and players such as televisions, set-top boxes, music players, digitalphoto frames, and digital cameras). Additionally, the electronic systemcould be a host or a slave to the input device.

The input device 100 can be implemented as a physical part of theelectronic system, or can be physically separate from the electronicsystem. As appropriate, the input device 100 may communicate with partsof the electronic system using any one or more of the following: buses,networks, and other wired or wireless interconnections. Examples includeI2C, SPI, PS/2, Universal Serial Bus (USB), Bluetooth, RF, and IRDA.

In FIG. 1, the input device 100 is shown as a proximity sensor device(also often referred to as a “touchpad” or a “touch sensor device”)configured to sense input provided by one or more input objects 140 in asensing region 120. Example input objects include fingers and styli, asshown in FIG. 1.

Sensing region 120 encompasses any space above, around, in and/or nearthe input device 100 in which the input device 100 is able to detectuser input (e.g., user input provided by one or more input objects 140).The sizes, shapes, and locations of particular sensing regions may varywidely from embodiment to embodiment. In some embodiments, the sensingregion 120 extends from a surface of the input device 100 in one or moredirections into space until signal-to-noise ratios prevent sufficientlyaccurate object detection. The distance to which this sensing region 120extends in a particular direction, in various embodiments, may be on theorder of less than a millimeter, millimeters, centimeters, or more, andmay vary significantly with the type of sensing technology used and theaccuracy desired. Thus, some embodiments sense input that comprises nocontact with any surfaces of the input device 100, contact with an inputsurface (e.g. a touch surface) of the input device 100, contact with aninput surface of the input device 100 coupled with some amount ofapplied force or pressure, and/or a combination thereof. In variousembodiments, input surfaces may be provided by surfaces of casingswithin which the sensor electrodes reside, by face sheets applied overthe sensor electrodes or any casings, etc. In some embodiments, thesensing region 120 has a rectangular shape when projected onto an inputsurface of the input device 100.

The input device 100 may utilize any combination of sensor componentsand sensing technologies to detect user input in the sensing region 120.The input device 100 comprises one or more sensing elements fordetecting user input. For example, the input device 100 may usecapacitive techniques, where voltage or current is applied to create anelectric field. Nearby input objects cause changes in the electricfield, and produce detectable changes in capacitive coupling that may bedetected as changes in voltage, current, or the like.

One exemplary capacitive technique utilizes “mutual capacitance” sensingmethods based on changes in the capacitive coupling between sensorelectrodes. In various embodiments, an input object near the sensorelectrodes alters the electric field between the sensor electrodes, thuschanging the measured capacitive coupling. In one implementation, asensing method operates by detecting the capacitive coupling between oneor more transmitter sensor electrodes (also “transmitter electrodes” or“TX electrodes”) and one or more receiver sensor electrodes (also“receiver electrodes” or “RX electrodes”). Transmitter sensor electrodesmay be modulated relative to a reference voltage to transmit transmittersignals. In various embodiments, the reference voltage may be asubstantially constant voltage, or the reference voltage may be systemground. The transmitter electrodes are modulated relative to thereceiver electrodes to transmit transmitter signals and to facilitatereceipt of resulting signals. A resulting signal may comprise effect(s)corresponding to one or more transmitter signals, and/or to one or moresources of environmental interference (e.g. other electromagneticsignals). Sensor electrodes may be dedicated transmitters or receivers,or may be configured to both transmit and receive.

It will be appreciated that embodiments described herein are also usablein environments utilizing “self-capacitance” techniques.“Self-capacitance” (or “absolute capacitance”) sensing methods are basedon changes in the capacitive coupling between sensor electrodes and aninput object. In various embodiments, an input object near the sensorelectrodes alters the electric field near the sensor electrodes, thuschanging the measured capacitive coupling. In one implementation, anabsolute capacitance sensing method operates by modulating sensorelectrodes with respect to a reference voltage (e.g. system ground), andby detecting the capacitive coupling between the sensor electrodes andinput objects.

In FIG. 1, a processing system 110 is shown as part of the input device100. The processing system 110 is configured to operate the hardware ofthe input device 100 to detect input in the sensing region 120. Theprocessing system 110 comprises parts of or all of one or moreintegrated circuits (ICs) and/or other circuitry components. Forexample, a processing system for a mutual capacitance sensor device maycomprise transmitter circuitry configured to transmit signals withtransmitter sensor electrodes, and/or receiver circuitry configured toreceive signals with receiver sensor electrodes. In some embodiments,the processing system 110 also comprises electronically-readableinstructions, such as firmware code, software code, and/or the like. Insome embodiments, components composing the processing system 110 arelocated together, such as near sensing element(s) of the input device100. In other embodiments, components of processing system 110 arephysically separate with one or more components close to sensingelement(s) of input device 100, and one or more components elsewhere.For example, the input device 100 may be a peripheral coupled to acomputing device, and the processing system 110 may comprise softwareconfigured to run on a central processing unit of the computing deviceand one or more ICs (e.g., with associated firmware) separate from thecentral processing unit. As another example, the input device 100 may bephysically integrated in a mobile device, and the processing system 110may comprise circuits and firmware that are part of a main processor ofthe mobile device. In some embodiments, the processing system 110 isdedicated to implementing the input device 100. In other embodiments,the processing system 110 also performs other functions, such asoperating display screens, driving haptic actuators, etc.

The processing system 110 may be implemented as a set of modules thathandle different functions of the processing system 110. Each module maycomprise circuitry that is a part of the processing system 110,firmware, software, or a combination thereof. In various embodiments,different combinations of modules may be used. Example modules includehardware operation modules for operating hardware such as sensorelectrodes and display screens, data processing modules for processingdata such as sensor signals and positional information, and reportingmodules for reporting information. Further example modules includesensor operation modules configured to operate sensing element(s) todetect input, identification modules configured to identify gesturessuch as mode changing gestures, and mode changing modules for changingoperation modes. In one or more embodiments, a first and second modulemay be comprised in separate integrated circuits. For example, a firstmodule may be comprised at least partially within a first integratedcircuit and a separate module may be comprised at least partially withina second integrated circuit. Further, portions of a single module mayspan multiple integrated circuits.

In some embodiments, the processing system 110 responds to user input(or lack of user input) in the sensing region 120 directly by causingone or more actions. Example actions include changing operation modes,as well as GUI actions such as cursor movement, selection, menunavigation, and other functions. In some embodiments, the processingsystem 110 provides information about the input (or lack of input) tosome part of the electronic system (e.g. to a central processing systemof the electronic system that is separate from the processing system110, if such a separate central processing system exists). In someembodiments, some part of the electronic system processes informationreceived from the processing system 110 to act on user input, such as tofacilitate a full range of actions, including mode changing actions andGUI actions.

For example, in some embodiments, the processing system 110 operates thesensing element(s) of the input device 100 to produce electrical signalsindicative of input (or lack of input) in the sensing region 120. Theprocessing system 110 may perform any appropriate amount of processingon the electrical signals in producing the information provided to theelectronic system. For example, the processing system 110 may digitizeanalog electrical signals obtained from the sensor electrodes. Asanother example, the processing system 110 may perform filtering orother signal conditioning. As yet another example, the processing system110 may subtract or otherwise account for a baseline, such that theinformation reflects a difference between the electrical signals and thebaseline. As yet further examples, the processing system 110 maydetermine positional information, recognize inputs as commands,recognize handwriting, and the like.

“Positional information” as used herein broadly encompasses absoluteposition, relative position, velocity, acceleration, and other types ofspatial information. Exemplary “zero-dimensional” positional informationincludes near/far or contact/no contact information. Exemplary“one-dimensional” positional information includes positions along anaxis. Exemplary “two-dimensional” positional information includesmotions in a plane. Exemplary “three-dimensional” positional informationincludes instantaneous or average velocities in space. Further examplesinclude other representations of spatial information. Historical dataregarding one or more types of positional information may also bedetermined and/or stored, including, for example, historical data thattracks position, motion, or instantaneous velocity over time.

In some embodiments, the input device 100 is implemented with additionalinput components that are operated by the processing system 110 or bysome other processing system. These additional input components mayprovide redundant functionality for input in the sensing region 120, orsome other functionality. FIG. 1 shows buttons 130 near the sensingregion 120 that can be used to facilitate selection of items using theinput device 100. Other types of additional input components includesliders, balls, wheels, switches, and the like. Conversely, in someembodiments, the input device 100 may be implemented with no other inputcomponents.

In some embodiments, the input device 100 comprises a touch screeninterface, and the sensing region 120 overlaps at least part of anactive area of a display screen. For example, the input device 100 maycomprise substantially transparent sensor electrodes overlaying thedisplay screen and provide a touch screen interface for the associatedelectronic system. The display screen may be any type of dynamic displaycapable of displaying a visual interface to a user, and may include anytype of light emitting diode (LED), organic LED (OLED), cathode ray tube(CRT), liquid crystal display (LCD), plasma, electroluminescence (EL),or other display technology. The input device 100 and the display screenmay share physical elements. For example, some embodiments may utilizesome of the same electrical components for displaying and sensing. Invarious embodiments, one or more display electrodes of a display devicemay configured for both display updating and input sensing. As anotherexample, the display screen may be operated in part or in total by theprocessing system 110.

It should be understood that while certain embodiments are described inthe context of a fully functioning apparatus, the mechanisms describedherein are capable of being distributed as a program product (e.g.,software) in a variety of forms. For example, the mechanisms may beimplemented and distributed as a software program on information bearingmedia that are readable by electronic processors (e.g., non-transitorycomputer-readable and/or recordable/writable information bearing mediareadable by the processing system 110). Additionally, other types ofmedia may be used to carry out the distribution. Examples ofnon-transitory, electronically readable media include various discs,memory sticks, memory cards, memory modules, and the like.Electronically readable media may be based on flash, optical, magnetic,holographic, or any other storage technology.

FIG. 2 illustrates a block diagram 200 of another exemplary environment.Included is an example of a biometric sensor 210 for sensing abiometric, such as a fingerprint from a user finger 220. The sensor maybe formed on the surface of a top glass 212, which may be part of adisplay screen, such as a touch screen. The sensor for a biometric orfingerprint sensor may be implemented, for example, using differentialreadout schemes as described herein. In other embodiments, the sensormay be located on a button, or in a dedicated fingerprint sensinglocation. According to the illustrated embodiment, on the underside ofthe glass layer 212 over which the finger 220 of the user may be placedor swiped, may be formed a layer 214 of material, which may be adielectric and may be flexible, such as a film of Kapton® tape, whichmay have sensor element electrodes/traces formed on one or both opposingsurfaces and may also have mounted thereon, e.g., by a chip on film(COF) or flip chip mounting technique, a sensor controller IC 216 to thesubstrate containing the sensor element electrodes/traces. As noted inthis application, for some embodiments, the entire assembly may be onthe order of less than 1 mm in thickness H, e.g., on the order of 0.1 mmin thickness, especially for COF types of packaging when consideredwithout the thickness of the IC, such as when the IC is separate fromthe sensor. Also, depending on acceptable signal level, the thicknessmay be on the order of 2 mm or even thicker, e.g., for flip chipmounting packages. While one implementation of a fingerprint sensor isillustrated in FIG. 2, it should be appreciated that sensors accordingto the exemplary embodiments described herein may be beneficiallyutilized in a wide variety of fingerprint sensor designs andimplementations.

FIGS. 3A and 3B illustrate an exemplary implementation for a processingsystem 300 that utilizes a pattern-dependent reference. In thisimplementation, when a particular pixel on a transmission line (or“transmitter sensor electrode”) is read on a particular receiver line(or “receiver sensor electrode”), the reading on that receiver line iscompared with the average of readings on the other receiver linescorresponding to sensing signals driven on the same transmission line toobtain an output for that coordinate. Specifically, as illustrated inFIG. 3A, when obtaining an output at the pixel where the firsttransmission line (TX1) overlaps with the first receiver line (RX1), adifference between the reading on RX1 and the average of the readings onRX2-RX6 (the average is produced by shorting the receiver lines RX2-RX6together) is obtained and amplified via a low-noise amplifier (LNA) 301.Similarly, as illustrated in FIG. 3B, when obtaining an output at thepixel where the first transmission line (TX1) overlaps with the secondreceiver line (RX2), a difference between the reading on RX1 and theaverage of the readings on RX1 and RX3-RX6 is obtained and amplified viaa LNA 302. It will be appreciated that, although switches are not shownin FIGS. 3A and 3B, the different communication pathways illustrating inFIGS. 3A and 3B are established through the synchronized use of switcheswith respective receiver lines being read.

The configuration shown in FIGS. 3A-3B using a pattern-dependentreference allows the processing system to obtain an output at particularpixels that reduces environmental noise (since the same environmentalnoise is present at the receiver line for the pixel being read as ispresent at the other receiver lines). However, the use of thepattern-dependent reference may introduce distortions into the detectedimage. For example, in a fingerprint sensor, when a ridge or a valley onthe fingerprint spans all of the receiver lines, there may be nodifference between the reading on one receiver line and the average ofthe rest of the receiver lines, such that the fingerprint sensor isunable to determine whether a ridge or a valley is present. Such imagedistortions cannot be corrected by baseline image subtraction, codedivision multiplexing (CDM), or measuring temporal noise.

It will be appreciated that FIG. 3 also illustrates a portion of anexemplary processing circuit 330, including components such as the LNAs301 and 302, MUXs 310 and 311, and VGAs 320 and 321. It will further beappreciated that the processing circuit 330 may be a part of a sensorchip.

FIG. 4 illustrates a processing system 400 that utilizes a fixedreference in accordance with an exemplary embodiment. In the processingsystem 400, when a particular pixel on a transmission line is read by aparticular receiver electrode, the reading on that receiver linecorresponding to sensing signals driven on a transmission line iscompared with a reading on a reference receiver line (or “referencereceiver electrode”) corresponding to sensing signals driven on areference transmission line (or “reference transmitter electrode”) toobtain an output for that coordinate. Specifically, as illustrated inFIG. 4, when obtaining an output at the pixel where the firsttransmission line (TX1) overlaps with the first receiver line (RX1), adifference between the reading on RX1 and a corresponding reading onRXref (at a fixed reference point where a reference transmission line(TXref) overlaps with the reference receiver line (RXref)) is obtainedand amplified via a low-noise amplifier (LNA) 401. The output at otherpixels is similarly obtained by comparing readings on respectivereceiver lines with corresponding readings at the fixed reference point.

It will be appreciated that FIG. 4 also illustrates a portion of anexemplary processing circuit 430, including components such as the LNAs(401), MUXs (402), and VGAs (403).

It will be appreciated that each time sensing signals are driven onto aparticular transmission line to obtain a reading at a receiver lineoverlapping that transmission line, corresponding sensing signals(preferably of the same amplitude and shape) are also driven onto thetransmission reference line to obtain the reference reading on thereference receiver line.

Because the fixed reference point is on the same sensor plane as thepixels being read, using the difference between the reading at the fixedreference point and a pixel being read reduces or eliminatesenvironmental noise. Further, because a fixed reference point is beingused, each pixel of the array of receiver and transmission lines isbeing compared to the same reference. For example, for a fingerprintsensor, if a ridge is present at the fixed reference point, all pixelscorresponding to a frame being read out by the processing system andinput device are compared to the ridge. Similarly, if a valley ispresent at the fixed reference point, all pixels corresponding to aframe being read out by the processing system and input device arecompared to the valley. This provides a consistent reference thatproduces an image without image distortion, since every feature of thefingerprint is identifiable relative to the fixed reference point.

The exemplary configuration depicted in FIG. 4 includes one LNA for eachreceiver line. Having a large number of LNAs allows for fastperformance, but may increase cost, power consumption and space requiredfor the processing system. FIG. 5 illustrates a processing system 500that utilizes a fixed reference in accordance with an exemplaryembodiment that is relatively more efficient and lower-cost than theprocessing system 400 depicted in FIG. 4. In this exemplary embodiment,switches (illustrated in FIG. 5 as transistor switches) are added toeach receiver line. Controlling these switches in a synchronized mannerwith the sensing signals driven onto particular transmission lines andthe transmission reference line allows a differential output to beobtained for each pixel, relative to the fixed reference point, usingonly one LNA 501 for the entire array of transmission and receiverlines.

It will be appreciated that FIG. 5 also illustrates a portion of anexemplary processing circuit 530, including components such as an LNA501, VGA 502, Mixer 503, and Analog-to-Digital Converter (ADC) 504.

In further embodiments, where a faster reading speed (i.e., framerate)is desired, more LNAs can be added such that certain receiver lines canbe read in parallel via two or more LNAs. It will be appreciated thatthere is thus a tradeoff between cost-savings, circuit space/size andpower efficiency versus reading speed, and that, depending on the numberof LNAs used in combination with the fixed reference point, differentexemplary implementations are able to satisfy different speedrequirements while being relatively cost-, space- and power-efficientrelative to embodiments having unused LNAs.

FIGS. 6A-6B illustrates a processing system 600 that utilizes a fixedreference, with differential readouts between adjacent receiver lines,in accordance with another exemplary embodiment. FIG. 6A illustrates areading taken on a first receiver line RX1 corresponding to sensingsignals driven onto a second transmission line TX2. This first readingis obtained relative to a reference reading at the fixed reference point(corresponding to the transmission and receiver reference lines),similar to the discussed above with respect to FIG. 4. FIG. 6Billustrates a reading taken on a second receiver line RX2 correspondingto sensing signals driven onto the second transmission line TX2. Thissecond reading is obtained relative to a reading on the first receiverline RX1. Further readings on further receiver lines are also obtainedrelative to an adjacent preceding line (e.g., reading on RX3 is obtainedrelative to a reading on RX2, etc.). It will be appreciated that,although switches are not shown in FIGS. 6A and 6B, the differentcommunication pathways illustrating in FIGS. 6A and 6B are establishedthrough the synchronized use of switches with respective receiver linesbeing read.

This “adjacent differential readout” sensing technique generates“differential” results where the value of each pixel is obtainedrelative to a previous adjacent receiver line (or the fixed referencefor pixels on the first receiver line), which allows for a “differentialimage” to be generated based on pixel values corresponding to these“differential” results. On the other hand, the embodiments depicted inFIGS. 4-5 utilize a whole-frame fixed reference sensing technique, whichgenerates “absolute” results where the value of each pixel is obtainedrelative to the fixed reference point, which allows for an “absoluteimage” to be generated based on pixel values corresponding to these“absolute” results. While the “adjacent differential readout” sensingtechnique tends to generate relatively more temporal noise (since thefinal image needs to be reconstructed from the differential image thatis generated), the “adjacent differential readout” sensing technique issuitable for significantly reducing system noise with respect to largeformat systems, and allows for increased correlation of system noisebetween two adjacent receiver lines. For example, for relatively smallerpanels, using the whole-frame fixed reference sensing technique togenerate an “absolute image” can provide sufficiently precise removal ofsystem noise even where the receiver line being read and the referenceline are not adjacent (e.g., on opposing sides of the array). Forrelatively larger panels however, correlation of system noise between areceiver line and the reference line that are relatively far away fromeach other can become degraded, and thus using a “adjacent differentialreadout” technique in such situations may provide more favorableresults.

FIG. 7 illustrates a processing system 700 that utilizes a fixedreference, with differential readouts between adjacent receiver lines,in accordance with yet another exemplary embodiment that is relativelymore efficient in terms of cost, power consumption and space relative tothe processing system 600 depicted in FIGS. 6A-6B. The principles ofoperation of the processing system 700 are similar to processing system600 in that outputs on each subsequent receiver line is obtainedrelative to a previous adjacent receiver line, with the output for thefirst receiver line being obtained relative to a fixed reference point.However, because of the use of only one LNA 701 for the entire array ofreceiver and transmission lines (along with the depicted switchesallowing different receiver lines to be connected to the LNA), adifferential image for the entire array is obtainable with a lower-costand smaller sensor circuit and with less power consumption. Similar tothe principles discussed above with respect to FIG. 5, controlling theseswitches in a synchronized manner with the sensing signals driven ontoparticular transmission lines allows a differential output to beobtained for each pixel, relative to an adjacent receiver line (or thefixed reference point for the first receiver line), using only one LNAfor the entire array of transmission and receiver lines. Further,similar to the principles discussed above with respect to FIG. 5, wherea faster reading speed is desired, more LNAs than just the one depictedin FIG.7 can be utilized such that certain receiver lines can be read inparallel via two or more LNAs.

It will further be appreciated that the processing system 700 mayfurther be operated so as to utilize the whole-frame fixed referencesensing technique instead of the “adjacent differential readout” sensingtechnique by control of the switches such that, for each receiver linethat is read, the switch for that receiver line and the switch for thereference receiver line are turned on (with appropriate correspondingsensing signals driven onto the transmission line and referencetransmission line), such that each pixel is compared to the fixedreference point.

FIGS. 8A and 8B illustrate arrays 800 a and 800 b of receiver andtransmission lines for exemplary embodiments where a dedicated referencetransmitter electrode is not used. Instead, in these exemplaryembodiments, the reference receiver electrode overlaps with thetransmitter sensor electrodes such that the sensing signals driven ontoeach transmission line for obtaining a reading on a respective receiversensor electrode are also used to obtain a reference reading forcomparison.

FIG. 8A illustrates an exemplary embodiment where the array 800 aincludes a single reference receiver line that is adjacent to two groundshielding lines, which makes the reference receiver line less sensitiveto features of the finger such that, regardless of whether a ridge orvalley is present, a substantially constant reference signal (for eachtransmission line) may be produced on the reference receiver line when afinger is present on the sensor. Thus, the receiver lines from RX1onwards will be able to produce values for different features (i.e.,ridges and valleys) of a finger that are each different from theconstant reference signal, and the processing system for the sensor isable to identify the features of the finger based on the differencesbetween the detected values and the constant reference signal.

FIG. 8B illustrates an exemplary embodiment where the array 800 bincludes three reference receiver lines are used to obtain an averagereference reading by shorting the three lines together.

It will be appreciated that the location of the reference point in theembodiments depicted in FIGS. 8A and 8B change for each transmissionline, and that other embodiments may include features similar to thoseshown in FIGS. 8A and 8B while using a constant location for thereference point.

FIGS. 9A-9B illustrate an array 900 of receiver and transmission linesfor an exemplary embodiment where receiver and transmitter sensorelectrodes are also used as reference receiver and transmitterelectrodes, depending on which pixels of the array are being read.Specifically, FIG. 9A illustrates the array 900 while a top half of thearray is being read (e.g., for an array with 100 receiver lines, the tophalf may include the top 50 lines). For each pixel in the top half ofthe array, a certain transmitter sensor electrode of the bottom half ofthe array is used as a reference transmitter electrode, and a set ofreceiver sensor electrodes of the bottom half of the array is used a setof reference receiver electrodes. Conversely, FIG. 9B illustrates thearray 900 while a bottom half of the array is being read. For each pixelin the bottom half of the array, a certain transmitter sensor electrodeof the top half of the array is used as a reference transmitterelectrode, and a set of receiver sensor electrodes of the top half ofthe array is used a set of reference receiver electrodes. Thus, thearray 900 allows the use of a first fixed reference point (or area, whenmultiple reference receiver lines are used) for the top half of thearray, and the use of a second fixed reference point (or area) for thebottom half of the array.

In an exemplary embodiment, the transmitter electrodes used for the tophalf of the array are not the same as the transmitter electrodes used inthe bottom half of the array (in other words, the transmitter electrodesare disjointed as depicted in FIGS. 9A and 9B). Alternatively, inanother exemplary embodiment, the transmitter electrodes for the top andbottom halves are the same and are continuous. It will be appreciatedthat for either of the exemplary embodiments, either the whole-framefixed reference sensing technique or the “adjacent differential readout”sensing technique can be used to generate an image with respect to eachhalf of the array. Further, it will be appreciated that the portions ofthe array used as the reference need not be “halves” of the array, andmay be portions of the array including multiple receiver lines that areconfigured to be used as a reference for certain other receiver lines ofthe array.

FIGS. 10A and 10B illustrate processes 1000 a and 1000 b for producingan “absolute” image corresponding to detected signals using whole-framefixed reference sensing techniques. FIG. 10A illustrates a process 1000a corresponding to embodiments having a reference transmitter electrodethat is separate from a transmitter electrode being driven with respectto a corresponding receiver electrode (e.g., as depicted in FIGS. 4, 5,7 and 9A-9B). At stages 1001 and 1002, sensing signals are synchronouslydriven onto a reference transmitter electrode and a transmitterelectrode. In response thereto, a reference signal is obtained by areference receiver electrode at stage 1012, and a detected signal isobtained by a receiver electrode based on the transmitter electrode fora pixel to be read at stage 1011. At stage 1021, a modified detectedsignal is obtained for that pixel by processing the obtained detectedsignal and the reference signal (including a comparison of the obtaineddetected signal to the reference signal). This sensing process isrepeated for all pixels of the array to generate an “absolute” image atstage 1031.

The process 1000 b illustrated in FIG. 10B is similar to the process1000 a, except that process 1000 b corresponds to embodiments which donot have a separate reference transmitter electrode. Rather, theseembodiments utilize a single transmitter electrode to produce detectedsignals on both the reference receiver electrode and a receiverelectrode corresponding to a pixel to be read (e.g., as depicted inFIGS. 8A-8B and for an alternative embodiment of FIGS. 9A-9B). Thus, theprocess 1000 b is similar to process 1000 a except that a separate stagefor driving the separate reference transmitter electrode is not used. Asingle stage 1041 is used to drive sensing signals onto the transmitterelectrode to produce detected signals on both the reference receiverelectrode and a non-reference receiver electrode.

FIGS. 11A and 11B illustrate processes 1100 a and 1100 b for producing a“differential” image corresponding to detected signals using “adjacentdifferential readout” sensing techniques. FIG. 11A illustrates a process1100 a corresponding to embodiments having a reference transmitterelectrode that is separate from a transmitter electrode being drivenwith respect to a corresponding receiver electrode (e.g., as depicted inFIGS. 6A-6B, 7 and 9A-9B). At stages 1001 and 1002, sensing signals aresynchronously driven onto a reference transmitter electrode and atransmitter electrode. In response thereto, a reference signal isobtained by a reference receiver electrode at stage 1112 (in certainembodiments, the reference receiver electrode may be a part of the arrayand may be the first receiver electrode in the array and not a separatededicated reference receiver electrode), and a detected signal isobtained by a first receiver electrode adjacent to the referencereceiver electrode based on the transmitter electrode for the firstpixel to be read in a column at stage 1111. At stage 1121, a modifieddetected signal is obtained for that pixel by processing the obtaineddetected signal and the reference signal (including a comparison of theobtained detected signal to the reference signal).

For all subsequent pixels in the column, process 1100 a continues bydriving sensing signals onto the transmitter electrode at stage 1131.Detected signals corresponding to a current receiver electrode to beread and corresponding to a previous adjacent receiver electrode thatwas read are obtained at stages 1141 and 1142. At stage 1151, a modifieddetected signal is obtained for each subsequent pixel of the column byprocessing the obtained detected signal for the current receiverelectrode and the obtained detected signal for the previous adjacentreceiver electrode (including a comparison of the obtained detectedsignal to the reference signal).

This sensing process is applied to each pixel in each column of thearray, as depicted in FIG. 11A, to generate a “differential” image atstage 1161.

The process 1100 b illustrated in FIG. 11B is similar to the process1100 a, except that process 1100 b corresponds to embodiments which donot have a separate reference transmitter electrode. Rather, theseembodiments utilize a single transmitter electrode to produce detectedsignals on both the reference receiver electrode and a receiverelectrode corresponding to a first pixel to be read in a column (e.g.,as depicted in FIGS. 8A-8B and for an alternative embodiment of FIGS.9A-9B). Thus, the process 1100 b is similar to process 1100 a exceptthat a separate stage for driving the separate reference transmitterelectrode is not used. A single stage 1171 is used to drive sensingsignals onto the transmitter electrode to produce detected signals onboth the reference receiver electrode and a non-reference receiverelectrode.

FIG. 12 is a schematic diagram of an array 1200 of receiver andtransmission lines for a processing system for an input device in anexemplary embodiment utilizing split-drive differential sensing (similarto the embodiment depicted above with respect to FIGS. 9A-9B). Each ofthe transmitter electrodes of the array 1200 comprises a first portionand a second portion, with a separation between the first portion andthe second portion. For example, with respect to transmitter electrode1210, the first portion 1211 and the second portion 1212 are separatedby the separation 1213. The separation isolates the first portion 1211from the second portion 1212 so that they are not in ohmic contact witheach other, allowing them to be separately driven with signals. It willbe appreciated that although the transmitter electrode 1210 is referredto herein as a single electrode, the transmitter electrode 1210 may alsobe understood as multiple separate electrodes (e.g., one electrodecorresponding to the first portion 1211 and another electrodecorresponding to the second portion 1212) that form a transmission linefor the array 1200. For simplicity, the separate electrode portions willbe referred to herein as being a transmitter electrode 1210 comprisingtwo portions 1211 and 1212 separated by the separation 1213.

FIG. 12 further depicts exemplary differential amplifiers 1231 and 1232connected to exemplary receiver electrodes 1221, 1222, 1223 and 1224. Inthe illustrated example, the first differential amplifier 1231 comparesresulting signals from receiver electrode 1221 overlapping with thefirst portion 1211 of the transmitter electrode 1210 with resultingreference signals from receiver electrode 1223 overlapping with thesecond portion 1212 of the transmitter electrode 1210. Similarly, thesecond differential amplifier 1232 compares resulting signals fromreceiver electrode 1222 overlapping with the first portion 1211 of thetransmitter electrode 1210 with resulting reference signals fromreceiver electrode 1224 overlapping with the second portion 1212 of thetransmitter electrode 1210.

In operation, when pixels corresponding to first portions of thetransmitter electrodes of the array are being read, one or more of thefirst portions of the transmitter electrodes are driven with transmittersignals while the second portions of the transmitter electrodes aregrounded (or held at some other fixed voltage). The presence of theobject being sensed, such as a user's finger, introduces a consistentamount of object-coupled noise (e.g., finger-coupled noise) to pixelscorresponding to both portions of the transmitter electrodes. Thus, whenresulting signals from a receiver electrode (e.g., receiver electrode1221) corresponding to a first portion of a transmitter electrode thatis driven (e.g., first portion 1211 of transmitter electrode 1210) arecompared with resulting reference signals from a receiver electrode(e.g., receiver electrode 1223) corresponding to a second portion of atransmitter electrode that is grounded (e.g., second portion 1212 oftransmitter electrode 1210) by a differential amplifier (e.g.,differential amplifier 1231), a modified resulting signal is determinedwith respect to a pixel being read for which the object-coupled noise iseffectively removed. Further, because a large number of receiver linesmay be used as reference channels for parallel measurement, a relativelystrong signal (e.g., corresponding to multiple receiver lines andmultiple reference receiver lines being read in parallel) can beobtained with respect to under-glass sensing applications (allowing forrelatively shorter measurement times or for more time to be spent forparticular pixels in a given capture time relative to sequentialmeasurement techniques).

Once pixels corresponding to the first portions of the transmitterelectrodes have been read, the driving status of the top and bottomhalves of the sensor array may be swapped such that the first portionsof the transmitter electrodes are grounded while the second portions ofthe transmitter electrodes are driven with transmitter signals. Thisallows the pixels corresponding to the second portions to be read whileremoving object-coupled noise based on reference readings from receiverelectrodes overlapping the first portions of the transmitter electrodes.By determining modified resulting signals for the pixels of the array,for example, using steps similar to those discussed above with respectto FIGS. 10A-10B and 11A-11B, sufficient data for generating an image ofthe object being sensed can be obtained.

While the pixels are being read, resulting signals corresponding topixels from one or multiple transmission lines (e.g., in the exampledepicted in FIG. 12, multiple transmitter electrode portions from oneside of the array) can be obtained simultaneously by driving one or moretransmission lines at a time. Thus, in different exemplary embodiments,the driving scheme for the portions of the transmitter electrodes beingdriven may include one transmission line being driven at a time, twotransmission lines being driven at a time, or more than two transmissionlines being driven at a time.

In certain exemplary embodiments, for example certain embodiments usingCDM schemes, all transmission lines may be simultaneously driven withvarious phase configurations (e.g., a certain number of transmissionlines being driven with transmitter signals having a first phase whilethe other transmission lines are driven with transmitter signals havinga second phase) in multiple steps according to a sequence. The sequenceincludes stepping through different combinations of transmission lineshaving different phases, and the readings obtained via the receiverlines are then processed by a processing system based on the phasesequencing to generate an image of the object being sensed.

With respect to the exemplary array depicted in FIG. 12, multipletransmitter electrode portions from one side of the array aresimultaneously driven while the transmitter electrode portions from theother side of the array are grounded or held to some other fixedvoltage. In other exemplary embodiments, such as those discussed belowwith respect to FIGS. 16, 17A-C and 18A-B, transmitter electrodeportions from both sides of the array may simultaneously be driven aswell.

FIG. 13 is a schematic diagram of an array 1300 of receiver andtransmission lines for a processing system for an input device inanother exemplary embodiment utilizing split-drive differential sensing.The transmitter electrodes each include a first portion and a secondportion separated via a separation formed in triangular patterns. Forexample, the first portion 1311 of the transmitter electrode 1310 isseparated from the second portion 1312 of the transmitter electrode viathe separation 1313, where the separation 1313 includes a triangularpattern. The triangular pattern of the separation 1313 makes the effectsof the structural transition from the first portion 1311 to the secondportion 1312 more gradual, which reduces the edge effects at the ends ofthe first and second portions at the separation 1313 relative to, forexample, the array 1200 of FIG. 12, which utilizes a horizontalseparation. In this manner, less signal loss is achieved on receiverlines near the separation 1313.

FIG. 14 is a schematic diagram of an array 1400 of receiver andtransmission lines for a processing system for an input device inanother exemplary embodiment utilizing split-drive differential sensing.The transmitter electrodes each include a first portion and a secondportion separated such that the first and second portions form aninterdigitated pattern. For example, the first portion 1411 of thetransmitter electrode 1410 is separated from the second portion 1412 ofthe transmitter electrode via the separation 1413, such that respectiveinterleaved protrusions of the first and second portions, separated bythe separation 1413, form the depicted interdigitated pattern. Similarto the array 1300 of FIG. 13, the interdigitated pattern makes theeffects of the structural transition from the first portion 1411 to thesecond portion 1412 more gradual, such that less signal loss is achievedon receiver lines near the separation 1413. The interdigitated patternof FIG. 14 provides for reduction of edge effects at pixels near theseparation 1413 (although area-wise, each portion of the transmitterelectrode forms around half of the total interdigitated portion, whenonly one half is being driven, the electrical field generated by thathalf is greater than half of what would be generated by a solidtransmission electrode being driven due to fringing effects).

It will be appreciated the horizontal, triangular, and interdigitatedseparation patterns between portions of the transmitter electrodes, withthe patterns being uniformly repeated for all transmission lines, asillustrated in FIGS. 12-14, are merely illustrations of exemplaryembodiments. Other exemplary embodiments may utilize differentseparation patterns between portions of the transmitter electrodes,which may or may not be uniformly repeated with respect to alltransmitter electrodes of the array.

It will further be appreciated that the separation between the first andsecond portions of the transmitter electrodes may be disposed betweentwo adjacent receiver electrodes (e.g., as depicted in FIGS. 12 and 13)or may be disposed so as to overlap with the two adjacent receiverelectrodes (e.g., as depicted in FIG. 14). Additionally, in certainexemplary embodiments, receiver lines that are near or that overlap withthe separations between transmitter electrodes are not used as referencereceiver lines; only receiver lines that are relatively farther from theseparation are used as reference receiver lines.

FIG. 15 is a schematic diagram of an array 1500 of receiver andtransmission lines for a processing system for an input device inanother exemplary embodiment utilizing split-drive differential sensing.FIG. 15 further depicts exemplary differential amplifiers 1531, 1532 and1533 connected to exemplary receiver electrodes 1521, 1522, 1523, 1524,1525 and 1526. While the top half of the array 1500, which correspondsto the first portions of the transmitter electrodes, is being driven andreadings are being obtained with respect to pixels of the top half ofthe array 1500 in FIG. 15, the first differential amplifier 1531receives resulting signals from receiver electrode 1521 via a firstinput and receiver reference signals from a combination of receiverelectrodes 1524, 1525 and 1526 via a second input. The seconddifferential amplifier 1532 and third differential amplifier 1533similarly receive first inputs from respective single receiverelectrodes 1522 and 1523 and receive second inputs from the combinationof receiver electrodes 1524, 1525 and 1526. Thus, while the bottom halfof the array 1500, which corresponds to the second portions of thetransmitter electrodes in FIG. 15, is being used to provide referencesignals for eliminating object-coupled noise, several receiver lines arecombined together to provide a shared reference that is utilized bymultiple differential amplifiers of the processing system correspondingto the array 1500.

In certain exemplary embodiments, the number of differential amplifiersused by the processing system is based on the number of referencereceiver electrodes combined together to provide the shared reference.For example, in FIG. 15, because three reference receiver electrodes aretied together to provide the shared reference, the processing systemutilizes three differential amplifiers so as to provide good matchingbetween the respective inputs of the differential amplifiers.

It will be appreciated that the number of reference receiver lines usedto provide the reference may vary in different embodiments, includingembodiments that use only one reference receiver electrode to providethe references as well as embodiments that use any number of referencereceiver electrodes up to the full number of receiver electrodesoverlapping a particular portion of the transmitter electrode. Incertain exemplary embodiments using a reference comprised of acombination of reference receiver electrodes, receiver electrodes thatare adjacent to or relatively close to the separation between theportions of the transmitter electrodes are not used to provide thecombined reference.

FIG. 16 is a schematic diagram of an array 1600 of receiver andtransmission lines for a processing system for an input device inanother exemplary embodiment utilizing split-drive differential sensing.FIG. 16 further depicts both sides of the array 1600 being provided bydriving voltages. In the particular example depicted in FIG. 16, allnine transmission lines (1610, 1620, 1630, 1640, 1650, 1660, 1670, 1680,1690) are driven with transmitter signals on the top portions of thetransmission lines, with different coded phases (“+” and “−”) beingprovided to the respective transmission lines. At the same time, threeof the transmission lines (1630, 1650, 1670) are also driven withreference transmitter signals on bottom portions of the transmissionlines (1632, 1652, 1672). The other bottom portions (such as bottomportion 1612) are grounded. Providing the reference portion of the array1600 with reference transmitter signals allows for a stronger signallevel to be achieved, which is particularly advantageous, for example,with respect to under-glass sensing applications.

As discussed above, the top portions of the transmission lines aresimultaneously driven with various phase configurations in multiplesteps according to a sequence. The sequence includes stepping throughdifferent combinations of phases for the top portions of thetransmission lines. During the entire sequence in which the drivingstatus of the top portions of the transmission lines is changing, thebottom portion is driven the same way—i.e., in a fixed manner. Thus, forexample, with respect to FIG. 16, the depicted “+−+−−−+−−” drivingstatus for the top portion corresponds to just one step and a differentconfiguration of phases may be used in a next step, while the drivingstatus for the bottom portion with bottom portions 1632, 1652 and 1672being driven as “−−−” remains the same for all steps of the sequence.This provides a consistent reference that allows for object-couplednoise to be subtracted out via the processing system.

In certain embodiments, the summation of the phases being used to drivethe top portions should be maintained to be the same as that of thephases being used to drive the bottom portions. Thus, for example withrespect to the configuration shown in FIG. 16, the summation of the topportion, which includes 6 transmitter electrode portions driven by “−”transmission signals and 3 transmitter electrode portions driven by “+”transmission signals, has a total summation of 3 “−”. The summation forthe bottom portion, which includes 3 reference transmitter electrodeportions being driven by “−” reference transmission signals, similarlyhas a total summation of 3 “−”.

In other examples, a different combination of “+” and “−” transmissionsignals having a different summation can be used for the top portionand/or the bottom portion—for example, the bottom portion could include3 reference transmitter electrode portions being driven by “−” referencetransmission signals and 2 reference transmitter electrode portionsbeing driven by “+” reference transmission signals (summation of 1 “−”)and be used in combination with the top portion configuration having 5transmitter electrode portions being driven by “−” transmission signalsand 4 transmitter electrode portions being driven by “+” transmissionsignals (also a summation of 1 “−”).

It will be appreciated that the coded phase or CDM techniques discussedabove for driving the transmission lines are not limited to split-drivedifferential sensing configurations and that they can also be used incombination with transmission electrodes that are not separated intomultiple portions.

For ease of understanding, certain features of the embodiments discussedabove have been described independently of one of another with respectto each figure. However, it will be appreciated that these features maybe used together in various embodiments. For example, in one exemplaryembodiment, the combined reference feature depicted in FIG. 15 isutilized together with the multiple simultaneous driving of both sidesof the array depicted in FIG. 16, as well as with the interdigitatedpattern depicted in FIG. 14. Other exemplary embodiments include variousother combinations of the features described herein as well.

It will further be appreciated that, although FIGS. 12-16 generallydepict the split-drive differential sensing configurations as havingfirst and second portions of transmitter electrodes being of equal sizeand having an equal number of receiver electrodes associated therewith,this is not a requirement. Other embodiments utilizing split-drivedifferential sensing may include transmitter electrodes having first andsecond portions of different sizes, as well as transmitter electrodesdivided into more than just two portions.

FIGS. 17A-C are schematic diagrams of an array 1700 of receiver andtransmission lines for a processing system for an input device inanother exemplary embodiment utilizing split-drive differential sensingshowing an exemplary way of operating the array to obtain readings forthe top half of the array. Similar to the exemplary embodiment shown inFIG. 9A, a single second portion of a first transmitter electrode (TX1)in the bottom half of the array is used as a reference. This singlesecond portion of the first transmitter electrode (TX1) is driven with areference transmitter signal, which allows resulting reference signalsto be obtained via the corresponding receiver electrodes. Additionally,the resulting reference signals from multiple reference receiver linesmay be connected together to provide an averaged reference taking intoaccount the readings from multiple receiver electrodes.

FIG. 17A illustrates the first portion of the first transmitterelectrode (TX1) being driven such that resulting signals for pixelscorresponding to the first portion of the first transmitter electrode(TX1) can be obtained. FIG. 17B illustrates the first portion of asecond transmitter electrode (TX2) being driven such that resultingsignals for pixels corresponding to the first portion of the secondtransmitter electrode (TX2) can be obtained. FIG. 17C illustrates thefirst portion of a third transmitter electrode (TX3) being driven suchthat resulting signals for pixels corresponding to the first portion ofthe third transmitter electrode (TX3) can be obtained. It can also beseen from FIGS. 17A-17C that the second portion of the first transmitterelectrode (TX1) is driven with reference transmitter signals so as toprovide consistent resulting reference signals with respect to all ofthe pixels corresponding to the first portions of the transmitterelectrodes that are being read (i.e., the pixels of the top portion ofthe array).

FIGS. 18A-C are schematic diagrams of the array 1700 showing anotherexemplary way of operating the array to obtain readings for the top halfof the array. In FIGS. 18A-C, second portions of two transmitterelectrodes (TX1 and TX2) are both driven with reference transmittersignals, and two first portions of two transmitter electrodes are drivenwith transmitter signals to allow for resulting signals to be obtainedsimultaneously for pixels corresponding to the two first portions of thetwo transmitter electrodes. Additionally, the resulting referencesignals from multiple reference receiver lines may be connected togetherto provide an averaged reference taking into account the readings frommultiple receiver electrodes.

FIG. 18A illustrates the first portions of the first and secondtransmitter electrodes (TX1 and TX2) being driven such that resultingsignals for pixels corresponding to the first portions of the first andsecond transmitter electrodes (TX1 and TX2) can be obtained. FIG. 18Billustrates the first portions of third and fourth transmitterelectrodes (TX3 and TX4) being driven such that resulting signals forpixels corresponding to the first portions of third and fourthtransmitter electrodes (TX3 and TX4) can be obtained. FIG. 18Cillustrates the first portions of (n−1)th and nth transmitter electrodes(TXn−1 and TXn) being driven such that resulting signals for pixelscorresponding to the first portions of (n−1)th and nth transmitterelectrodes (TXn−1 and TXn) can be obtained. It can also be seen fromFIGS. 18A-C that the second portions of the first and second transmitterelectrodes (TX1 and TX2) are driven with reference transmitter signalsso as to provide consistent resulting reference signals with respect toall of the pixels corresponding to the first portions of the transmitterelectrodes that are being read (i.e., the pixels of the top portion ofthe array).

In other exemplary embodiments, the array 1700 is operated with three ormore second portions of the transmitter electrodes being driven withreference transmitter signals to provide a consistent reference, with acorresponding amount of first portions of the transmitter electrodesbeing driven with transmitter signals to provide resulting signals forthe corresponding pixels. In these exemplary embodiments, thetransmitter electrode portions in the part of the array being used forreference is fixed regardless of which transmitter electrode portions inthe part of the array being read are driven. Additionally, the number oftransmitter electrode portions being driven for reference is preferablyequal to the number of transmitter electrode portions being driven toprovide pixel readings. This provides a similar signal level going intoeach input of the differential amplifier(s), such that the delta betweenthe inputs (corresponding to fingerprint information) is small, and ahigh gain can be applied to the delta.

In further exemplary embodiments, the array 1700 is driven using codedphase or CDM techniques. Similar to the embodiments discussed above withrespect to FIG. 16, the phases associated with the transmitter signalsdriving the part of the array 1700 being read go through a sequence ofdifferent phase configurations, while the phase configuration and thedriving configuration for the part of the array 1700 being used as thereference remains fixed. Additionally, in certain embodiments, the totalphase summation for the first portions of the transmitter electrodesbeing read equals the total phase summation for the second portions ofthe transmitter electrodes being used as the reference.

It will be appreciated that, although exemplary embodiments discussedherein depict rectangular transmitter and receiver electrodes arrangedin a grid pattern, the principles discussed herein with respect tosplit-drive sensing techniques may also be utilized with other electrodeconfigurations as well. One example is depicted in FIG. 19. FIG. 19illustrates an exemplary electrode configuration 1900 having electrodeswith “diamond” patterns, with a plurality of transmitter electrodes1910, 1920, 1930, 1940, 1950, 1960, 1970, 1980, 1990, each transmitterelectrode being separated into first and second portions (e.g., firstportion 1911 of transmitter electrode 1910 and second portion 1912 oftransmitter electrode 1910) that are divided by respective separations(e.g., the separation 1913 between first portion 1911 and second portion1912). In this exemplary configuration, the receiver electrodes formingthe receiver lines, which overlap the transmitter electrodes, also havediamond patterns, as depicted in FIG. 19. In the exemplary configuration1900 depicted in FIG. 19, the separation is positioned such that itbisects diamond patterns in the transmitter electrodes. This positioningof the separation can minimize any signal loss at pixels near theseparation portion. In other exemplary implementations relating toelectrodes having diamond patterns, the separation may be positioned ata different location (e.g., higher or lower in the relatively wide partsof the transmitter electrodes) and/or have a different shape (e.g.,similar to the different separation patterns discussed above withrespect to FIGS. 16-17).

The use of the terms “a” and “an” and “the” and “at least one” andsimilar referents in the context of the description and the claims areto be construed to cover both the singular and the plural, unlessotherwise indicated herein or clearly contradicted by context. The useof the term “at least one” followed by a list of one or more items (forexample, “at least one of A and B”) is to be construed to mean one itemselected from the listed items (A or B) or any combination of two ormore of the listed items (A and B), unless otherwise indicated herein orclearly contradicted by context. The terms “comprising,” “having,”“including,” and “containing” are to be construed as open-ended terms(i.e., meaning “including, but not limited to,”) unless otherwise noted.Recitation of ranges of values herein are merely intended to serve as ashorthand method of referring individually to each separate valuefalling within the range, unless otherwise indicated herein, and eachseparate value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (e.g., “such as”) provided herein, isintended merely to better illuminate the invention and does not pose alimitation on the scope of the invention unless otherwise claimed. Nolanguage in the specification should be construed as indicating anynon-claimed element as essential to the practice of the invention.

Variations of the exemplary embodiments discussed herein may becomeapparent to those of ordinary skill in the art upon reading theforegoing description. The inventors expect skilled artisans to employsuch variations as appropriate, and the inventors intend for theprinciples described herein to be practiced otherwise than asspecifically described herein. Accordingly, this invention includes allmodifications and equivalents of the subject matter recited in theclaims appended hereto as permitted by applicable law. Moreover, anycombination of the above-described elements in all possible variationsthereof is encompassed by the invention unless otherwise indicatedherein or otherwise clearly contradicted by context.

1. A device for capacitive sensing, comprising: a plurality of sensorelectrodes, the plurality of sensor electrodes comprising: a pluralityof receiver electrodes and a plurality of transmitter electrodes,wherein a transmitter electrode of the plurality of transmitterelectrodes comprises a first portion and a second portion with aseparation between the first portion and the second portion; and aprocessing system, configured to: drive the first portion of thetransmitter electrode with a transmitter signal, receive a resultingsignal corresponding to the first portion of the transmitter electrodevia a first receiver electrode of the plurality of receiver electrodes,receive a reference signal corresponding to the second portion of thetransmitter electrode via a second receiver electrode of the pluralityof receiver electrodes, and determine a modified resulting signal basedon the resulting signal and the reference signal.
 2. The deviceaccording to claim 1, wherein the sensor electrodes are arranged in agrid comprising rows of receiver electrodes and columns of transmitterelectrodes.
 3. The device according to claim 1, wherein the separationbetween the first portion and the second portion of the transmitterelectrode is disposed between two adjacent receiver electrodes of theplurality of receiver electrodes.
 4. The device according to claim 1,wherein the separation between the first portion and the second portionof the transmitter electrode is configured such that the first portionand the second portion of the transmitter electrode form aninterdigitated pattern.
 5. The device according to claim 4, wherein theseparation between the first portion and the second portion of thetransmitter electrode overlaps with two adjacent receiver electrodes ofthe plurality of receiver electrodes.
 6. The device according to claim1, wherein the separation between the first and the second portion ofthe transmitter electrode comprises a triangular pattern.
 7. The deviceaccording to claim 1, wherein the reference signal corresponding to thesecond portion of the transmitter electrode corresponds to the secondportion of the transmitter electrode being held at a fixed voltage. 8.The device according to claim 1, wherein each of the plurality oftransmitter electrodes comprises a first portion and a second portion;wherein the processing system is further configured to drive the firstportions of the plurality of transmitter electrodes according to asequence while driving at least one of the second portions of theplurality of transmitter electrodes with a reference transmitter signal.9. The device according to claim 8, wherein the sequence comprisesmultiple steps; wherein in each step of the multiple steps, multiplefirst portions of the plurality of transmitter electrodes are drivensimultaneously with coded phases corresponding to the step and referencetransmitter signals are applied to one or more second portions of theplurality of transmitter electrodes; and wherein for each step of themultiple steps a summation of phases of the multiple first portions isequal to a summation of phases of the one or more second portions. 10.The device according to claim 8, wherein the processing system isfurther configured to simultaneously drive an equal number of the firstportions and the second portions.
 11. The device according to claim 8,wherein the sequence comprises multiple steps; wherein in each step ofthe multiple steps, the reference transmitter signal used to drive theat least one of the second portions of the plurality of transmitterelectrodes remains fixed.
 12. The device according to claim 1, whereinthe processing system is further configured to receive another referencesignal from a third receiver electrode of the plurality of receiverelectrodes; and wherein determining the modified resulting signal isfurther based on a combination of the reference signal with the anotherreference signal.
 13. The device according to claim 1, wherein theprocessing system comprises multiple differential amplifiers, whereineach of the multiple differential amplifiers is configured to receive asan input reference signals corresponding to the second portion of thetransmitter electrode via multiple receiver electrodes of the pluralityof receiver electrodes, wherein the number of the multiple differentialamplifiers is equal to the number of the multiple receiver electrodes.14. The input device according to claim 1, wherein the processing systemcomprises a differential amplifier, wherein the differential amplifieris configured to perform the determination of the modified resultingsignal based on a differential of the resulting signal and the referencesignal.
 15. The device according to claim 1, wherein the plurality ofsensor electrodes are configured to detect ridges and valleys of afingerprint.
 16. A processing system for a capacitive sensing device,the processing system comprising a processor and a memory, wherein theprocessor is configured to: drive a first portion of a transmitterelectrode of the capacitive sensing device with a transmitter signal;receive a resulting signal corresponding to the first portion of thetransmitter electrode via a first receiver electrode of the capacitivesensing device; receive a reference signal corresponding to a secondportion of the transmitter electrode of the capacitive sensing devicevia a second receiver electrode of the capacitive sensing device, thesecond portion of the transmitter electrode being separate from thefirst portion of the transmitter electrode; and determine a modifiedresulting signal based on the resulting signal and the reference signal.17. The processing system according to claim 16, wherein the processoris further configured to drive first portions of a plurality oftransmitter electrodes of the capacitive sensing device according to asequence, and to drive at least one of a plurality of second portions ofthe plurality of transmitter electrodes of the capacitive sensing devicewith a reference transmitter signal.
 18. A method for capacitive sensingfor a capacitive sensing device, the method comprising: driving, by aprocessing system of the device, a first portion of a transmitterelectrode of the device with a transmitter signal; receiving, by theprocessing system, a resulting signal corresponding to the first portionof the transmitter electrode via a first receiver electrode of thedevice; receiving, by the processing system, a reference signalcorresponding to a second portion of the transmitter electrode of thedevice via a second receiver electrode of the device, the second portionof the transmitter electrode being separate from the first portion ofthe transmitter electrode; and determining, by the processing system, amodified resulting signal based on the resulting signal and thereference signal.
 19. The method according to claim 18, furthercomprising: driving first portions of a plurality of transmitterelectrodes of the device according to a sequence; and driving at leastone of a plurality of second portions of the plurality of transmitterelectrodes of the device with a reference transmitter signal.
 20. Themethod according to claim 18, further comprising: receiving anotherreference signal from a third receiver electrode; wherein determiningthe modified resulting signal is further based on a combination of thereference signal with the another reference signal.